From: Jason Gunthorpe <jgg@nvidia.com>
Date: Mon, 8 Jun 2026 18:10:04 +0000 (-0300)
Subject: iommu/dma: Do not try to iommu_map a 0 length region in swiotlb
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=6ec91df8aff77e2e8fe3179c1f3fc15b43a40ba3;p=thirdparty%2Flinux.git

iommu/dma: Do not try to iommu_map a 0 length region in swiotlb

iommu_dma_iova_link_swiotlb() processes a mapping that is unaligned in three
parts, the head, middle and trailer. If the middle is empty because there
are no aligned pages it will call down to iommu_map() with a 0 size
which the iommupt implementation will fail as illegal.

It then tries to do an error unwind and starts from the wrong spot
corrupting the mapping so the eventual destruction triggers a WARN_ON.

Check for 0 length and avoid mapping and use offset not 0 as the starting
point to unlink.

This is frequently triggered by using some kinds of thunderbolt NVMe
drives that trigger forced SWIOTLB for unaligned memory. NVMe seems to
pass in oddly aligned buffers for the passthrough commands from smartctl
that hit this condition.

Cc: stable@vger.kernel.org
Fixes: 433a76207dcf ("dma-mapping: Implement link/unlink ranges API")
Reported-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/0-v1-8536728bc89f+469-swiotlb_warn_jgg@nvidia.com
---

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 54d96e847f161..381b60d9e7cea 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1918,12 +1918,18 @@ static int iommu_dma_iova_link_swiotlb(struct device *dev,
 			return 0;
 	}
 
+	/*
+	 * After removing the partial head and tail, there may be no aligned
+	 * middle left to map.  The tail still gets bounced below.
+	 */
 	size -= iova_end_pad;
-	error = __dma_iova_link(dev, addr + mapped, phys + mapped, size, dir,
-			attrs);
-	if (error)
-		goto out_unmap;
-	mapped += size;
+	if (size) {
+		error = __dma_iova_link(dev, addr + mapped, phys + mapped,
+				size, dir, attrs);
+		if (error)
+			goto out_unmap;
+		mapped += size;
+	}
 
 	if (iova_end_pad) {
 		error = iommu_dma_iova_bounce_and_link(dev, addr + mapped,
@@ -1936,7 +1942,8 @@ static int iommu_dma_iova_link_swiotlb(struct device *dev,
 	return 0;
 
 out_unmap:
-	dma_iova_unlink(dev, state, 0, mapped, dir, attrs);
+	if (mapped)
+		dma_iova_unlink(dev, state, offset, mapped, dir, attrs);
 	return error;
 }